Recently, most chipsets have peripheral component interconnect express (PCIe) buses for high-speed data transmission. There are many cases where a redundant arrays of inexpensive disks (RAID) device includes a plurality of units. The units are connected by a midplane, a backplane, and a cable.
Housings are primarily connected by a cable. The type or length of the cable used in the connection between the housings is to be flexibly changed or selected depending on various conditions such as the scale-out number of the devices or an installation place.
Meanwhile, a characteristic difference due to the material, length, and type of the cable greatly influences the transmission quality of data. Thus, combinations of input and output settings of a PCIe switch with transmission characteristics of the cable are to be verified, and an optimum combination is to be previously selected. If an optimum value is not selected, there is a high possibility that a communication error will occur.
In general, the device (PCIe switch) that supports PCIe Gen3 has a function of automatically adjusting (auto-tuning) a setting value (waveform adjustment value) regarding a transmission waveform. The automatic adjustment is interactively performed between the devices.
In such an automatic adjustment, a value which falls within a prescribed value of an error rate and is capable of being linked up by PCIe is selected as a setting value. For example, Japanese Laid-open Patent Publication No. 9-331372, Japanese Laid-open Patent Publication No. 2008-42851, and Japanese Laid-open Patent Publication No. 2014-2637 are disclosed as related arts.
However, in an automatic setting method of setting an input and output setting value of the PCIe device of the related art stated above, a setting value determined through automatic setting at which an error rate approximates the prescribed value may be selected. That is, even though the setting value at which the error rate approximates the prescribed value is selected, it is determined that there is no problem in the transmission quality at the setting value, and connection is established in the device by using the setting value.
Accordingly, when an environment condition such as temperature or voltage is changed, since the device is not able to endure the environment change at the setting value at which the error rate approximates the prescribed value, there is a problem that a communication error occurs.
Thus, the cable used in the connection between the devices is limited, and a setting value prepared as an eigenvalue appropriated for the cable is set. However, in a case where the available cable is limited, a long cable is used even in the connection between adjacent devices, and thus, flexibility of the configuration using the communication cable is low, and there is a problem of inconvenience. In view of the foregoing, it is desirable that the likelihood of a transmission error occurring is low and communication quality is improved.